This disclosure relates generally to fluidic processing of samples for diagnostic purposes, sedimentation or centrifugal pelleting of suspended particulate matter, and quantifying analytes by addressing pelleted fractions of the sample. More specifically, this disclosure relates to direct processing and chemical analysis of raw biological samples, including analysis of food, soil, blood, stool, semen or other samples comprising solids or particulate matter.
A wide variety of techniques including immunoassay, nucleic acid hybridization, and enzymatic color change assays are used to chemically analyze samples of interest. To produce accurate and reproducible measurements, most assays employed for chemical analysis require specific environmental and chemical conditions. For instance, a precise temperature, precise concentration of reactants, a narrow range of salt concentrations, and an absence of interfering particulates or incidental chemicals may be necessary. Because a sample to be analyzed often does not meet these exacting specifications, laborious sample preparation may be necessary. These extra sample preparation procedures may increase labor costs and time delays associated with analysis.
One class of samples which causes particular problems in automated analysis are samples comprising solids, suspended particulate matter in liquid, and/or viscous liquids. Such samples include food, soil, blood, stool, motor oil, and semen. Conventional methods for preparing such samples for chemical analysis include pulverization of solids in the presence of a carrier liquid and centrifugation to remove suspended particles from a fluid for analysis.
A wide range of prior art surrounds the concept of integrating sample preparation into an automated chemical assay by way of a disk, cartridge or capillary tube which is spun to direct various reagent fluids and separate particulates from a sample of interest. One conventional method is the sedimentation assay in which suspended beads are used to bind an analyte of interest in the sample. The suspended beads and analyte are then sedimented through a density medium by centrifugation causing the particles to be separated from the sample. Conventional sedimentation assays were initially developed for radioimmunoassays where separation and shielding of the analyte from the rest of the unprocessed sample is necessary. Conventional sedimentation assays are capable of rapidly analyzing samples with minimum system complexity but are not well suited to processing samples with intrinsic heterogeneity or samples which comprise bulk solids.